Matrices for magnetic separators are known, for the separation of paramagnetic components such as hematite, ilmenite, wolframite, biotite, limonite, siderite, etc. from granular piles. Such matrices are used in the familiar induction-body magnetic separators of the most various designs (Jones Magnetic Separator, Humboldt-Wedag; German Fed. Rep. Publ. appln No. 1,132,062; Refining Technology (1973) 3, p. 142-149/Appendix; MIW Magnetic Separator England, Corporate Document of Boxmag-Rapid BR 18, HMC/4000/379; SALA HGMS of Zelesorudne bane Spisska Nova Ves, CSSR, Hornicka Primbram vo vede a technice, Symposium 18-22 Oct. 1982) in the form of strongly magnetizable grooved plates, profiled wires, expanded metal, steel wool, balls, rods, etc. All these matrices have in common that they have induction bodies of arbitrary geometric shape with strong curvatures on their surfaces. Consequently, they create high gradients in external magnetic fields which in turn lead to strong magnetic forces on particles in the neighborhood. The operating principle of these matrices in connection with magnetic separation is based on introducing a feed with a suitable concentration of solids between their induction bodies in the presence of a strong magnetic field. Due to the magnetic field and the high field gradients at the induction bodies, these more strongly paramagnetic, ferrimagnetic and ferromagnetic component of the pulp will deposit, while more weakly paramagnetic and diamagnetic components flow off freely. The magnetic particles adhering to the induction bodies are first washed in the magnetic field whereby an intermediate product is carried off, and after the washing process they are flushed out without a magnetic field, with a flush liquid under high pressure.
Ferromagnetic and ferrimagnetic admixtures in the feed, such as metal scraping or magnetite, sometimes adhere so rigidly to the induction bodies even without a magnetic field that even high water pressure is not sufficient to flush them out. This is caused especially by the remanence in conjunction with the strong curvatures at the surface of the induction bodies, because the residual magnetic force acting on the ferromagnetic and ferrimagnetic admixtures are all unreasonably high. As a consequence, the induction bodies become encrusted and must be cleaned or must be replaced prematurely, since the matrix otherwise blocks magnetically. Both measures require working time and entail considerable costs. Consequently, additional weak-field magnetic separators are frequently connected ahead of the induction bodies magnetic separators in order to separate ferromagnetic and ferrimagnetic admixtures.
Although the expense of reacting and operating these additional units is high, they do not really solve the problem, since the weak-field separators separate only a portion of the strongly magnetic admixtures of the charge material. Consequently, the magnetic blockage of the matrix is only delayed. Another disadvantage is the great space requirement and the need for several separation stages. In one case (German Democratic Republic patent No. 202,638), matrices of non-magnetic separation bodies in the shape of mutually parallel rods and plates, disposed perpendicularly to the field, have been proposed. The non-magnetic separation bodies can also be formed by structures consisting of wires or bulk material. If a charge material fed into such a matrix in a magnetic field, the more strongly magnetizable components of this material are retained in the field direction as chains of polarized particles between the non-magnetic separation bodies that are situated at a suitable distance, while weakly paramagnetic and diamagnetic components flow freely out of the matrix. After the magnetic field has been left behind or has been switched off, the polarization particle chains of paramagnetic particles decompose even if they are contaminated by strongly magnetic particles, and can be flushed out easily. A disadvantage here is that the type of separation remains limited purely to slurries, since the weak adhesive forces between the non-magnetic separation bodies and the polarization chains retain the latter only if they have a low mass, i.e., when their particles are very small. For example, in a matrix consisting of parallel aluminum plates at a 1 mm spacing, with an induction of 1.2T, hematite particles less than 10 .mu. can be separated from a pulp. Another disadvantage is that the separation of paramagnetic as well as ferromagnetic components is possible only when they exceed a certain minimum content in the charge, since otherwise no polarization particle chains can form. It is a further deficiency that, with respect to certain induction body matrices (e.g., groove plate-, expanded metal-, and ball matrices), about one furthermore ampere-turns requirement entails higher costs for more electric current and/or higher investment costs for coils with a larger number of windings in the separator.